The present invention relates to a method and device for protecting digital content, and more particularly to a digital copying method and storage device for digital content whereby the quality of the digital content deteriorates when a digital copy is made.
With the dissemination of information technology and the development of networks, the network transmission of digital content, such as music or still or moving images, has become very common. Copyright protection has become a problem of this transmission of digital content. When analog data is copied, the quality of the copy is degraded compared to that of the source. However, digital data can be copied many times with no deterioration of the quality. Consequently, there are no limits to the copying of digital data and it is possible to repeat the copying process and endlessly create data of the same quality as the original data. Moreover, with the realization of today's multi-functional PCs (personal computers), it has become possible to playback music and image content onto a personal computer. On a PC, it is possible to perform various operations that are not possible with devices exclusively for playing back content, such as CD or DVD players. The content data can be copied directly from the CD or DVD. Also, data that has been copied into the PC once can be easily produce many unauthorized copies.
Before now, music and image content was played with dedicated playback devices such as CD or DVD players. It was possible to control the permission to copy the digital content with the dedicated playback devices. For example, the content was encrypted and protected with CSS (Content Scramble System) on DVD. With encrypted content data, the content cannot be played back without a decryption key to cancel the encryption, even if removed directly from the medium. Also, with CGMS (Copy Generation Management System), copy generation management of the content can be performed so that copying from the original is permitted, but copying from a copy is not permitted.
In the case of the above mentioned methods, the copying of digital content has no flexibility and either a complete copy is possible or no copy can be made at all. Here, a complete copy is a copy of a quality such that the content user cannot perceive a difference in quality between the digital content of the copy source and the digital content of the copy destination. If there is no flexibility in the copying of digital content, such as if it were made impossible to make a copy from content data of a generation for which copying is not permitted, a user of the digital content might be limited in making copies for personal use, which was originally possible. It is possible to make a complete copy, for which the quality of the content is not changed at all, from content data of a generation for which copying is permitted. In the case of fraudulently repeating the copying process, however, this is a problem from the perspective of copyright protection.
There is a need for a method for copying digital content, to prevent digital copying of complete copies, for protecting the rights of the creators of digital content while supporting the desire of users to acquire digital content.